ATM1112 Engineering materials module 5 - Maysaa Nazar · 2018-10-02 · ATM 1112 – Engineering Materials Module 5: Compression Test 13 Activity 6 ... MT3037 Universal Testing machine

Engineering Materials

Module 5: Compression Test

PREPARED BY

IAT Curriculum Unit

August 2010

© Institute of Applied Technology, 2010

ATM 1112 – Engineering Materials

Module 5: Compression Test 2

Module 5: Compression Test Module Objectives

After the completion of this module, the student will be able to:

Explain the difference between compressive and shear forces.

Explain what the compressive test is and why do we perform it.

Follow the correct procedure to perform compression tests on aluminum, brass, copper and steel specimens.

Use the data obtained from a compression test to plot and analyse a stress-strain gragh.

Calculate the ultimate Compressive strength and modulus of elasticity for each tested material.

Module Contents Topic Page No.

1 The difference between compression and shear forces. 3

2 Compression test overview 4

3 Compression test procedures 6

4 Compression test results analysis 9

5 References 13


Compressive force

Connecting rod

Fig.5.1: An engine connecting rod under compressive forces.

Fig.5.2: Fastener under compressive forces.

Introduction

The compression test is the opposite of

the tensile test. Notice in Fig. 5.1 the

ends of the connecting rod are being

pushed toward each other,

“compressing” the part.

There are many situations in

manufacturing where parts are

subjected to compressive loads. An

example of a common compressive

load in manufacturing is a fastener

(Bolt) which holds two parts together.

This places a compressive force on the

parts as shown in Fig. 5.2.

Compression tests result in mechanical

properties that include the compressive

yield stress, compressive ultimate

stress, and compressive modulus of

elasticity.

1. The difference between

compressive and shear forces

A compressive force is a pushing force

where the force is perpendicular to the

surface of the material as shown in Fig.

5.2. While, the shear force is a cutting

force where the force is parallel to the

surface of the material as shown in Fig.

5.3. Accordingly, the direction of the force

applied will decide the type of stress on

the part.

Fig.5.3: Fastener under shear forces.



Activity 1:

Write an illustrative report to explain the various forms of stress applied on

engineering materials.

You can use the following links:

http://www.tpub.com/content/construction/14250/css/14250_14.htm

http://en.wikipedia.org/wiki/Stress_%28physics%29

http://www.ndt-ed.org/index_flash.htm

2. Compression test overview:

A compression test is performed on the

universal testing machine. The compression

space is situated at the lower end of the

safety plastic box of the machine as shown

in Fig 5.4.

Prior to the yield point tension and

compression results are similar. For some

ductile materials the specimen will compress

until a flat slug is reached as shown in Fig

5.5.

However, brittle materials will fail

immediately after their ultimate strength is

exceeded. These brittle materials have much

greater compression strength than tensile

strength. That is why they are mostly tested

under compression.

Concrete, wood and cast iron are examples

of materials mostly tested under

compression. For example the concrete

compressive strength is the most

important material property that

engineers consider when designing and

building a structure.

Fig. 5.4: Compression test portion on the universal testing machine.

Fig.5.5: A ductile material after the compression test.


http://www.tpub.com/content/construction/14250/css/14250_14.htm

http://en.wikipedia.org/wiki/Stress_%28physics%29

http://www.ndt-ed.org/index_flash.htm


2.1.The ultimate compressive strength:

The ultimate compressive strength is

the maximum compressive load

divided by the original cross sectional

area of the specimen.

Ultimate Compressive Strength

mm²)( )(

AreaOriginalNLoadMaximum

=

The piece of material to be tested is

placed in the provided place of the

machine for compression testing and

pushed until it bends. The test piece

first deforms elastically, then plastically.

See Fig.5.4.

Fig.5.4: A test piece is pushed until it bends.

2.2 Yield Point

The yield point during the compression test is reached at the exact moment

when the stress on a material exceeds the material’s elastic range as

explained earlier in module 4 (see Fig. 5.5).

2.3 Modulus of elasticity

The compressive modulus of elasticity is

usually higher than the tensile modulus of

elasticity and is greatly considered when

designing parts that will be subjected to

compressive forces.

As you can see in the stress/strain

diagram shown in Fig. 5.5, the stress and

strain are proportional within the elastic

range.

Elastic range

Straight line

Strain

Str

ess

Yield point

Fig.5.5: Stress-strain diagram for a material under compression.



The modulus of elasticity (Young’s modulus) can be calculated using the

following formula.

εσ

=Ε

Where E= modulus of elasticity in Kpa.

σ = Stress at the yield point in Kpa.

ε= Strain at the yield point.

3. Compression test procedures 1. Use the Vernier caliper to measure

the diameter of the specimen as

shown in Fig. 5.6 and record it.

Fig. 5.6: Measuring the diameter. 2. Switch on the machine as shown in

Fig. 5.7.

Fig. 5.7: The machine ON/OFF switch.

3. Place the specimen in the

compression test piece holders. Make

sure that the specimen is centered as

shown in Fig. 5.8.

Fig. 5.8: The specimen is fixed on the holder.



4. Reset the DL-indicator to zero as

shown in Fig. 5.9.

Fig. 5.9: Reset the DL-indicator. 5. Close the safety plastic door as shown

in Fig. 5.10.

Fig. 5.10: Secure the plastic door. 6. Adjust the cylinder speed by turning

the speed adjustment valve 1/16 of a

turn anticlockwise from the closed

position as shown in Fig. 5.11.

Fig. 5.11: Adjusting the speed valve.

7. Switch on the instrument panel and

make sure that the middle button is

set to PC as shown in Fig. 5.12.

Fig. 5.12: the instrument panel 8. Click the measuring display button as

shown in Fig. 5.13a, then click the

start button to start the test as shown

in Fig. 5.13b.

(a)

(b)

Fig. 5.13: (a) Measuring display button. (b) Measuring display box.



9. The machine starts and the cylinder moves slowly upwards while four

measurements of load and extension per seconds are being stored in a table as

shown in Fig. 5.15.

Important tips:

1) You need to STOP the compression test manually.

2) Do not compress more than shown in Fig 5.14.

5.14: The maximum compression limits for the test.

10. Record the maximum load that the specimen resisted.

11. Save the table and the graph as shown in Fig. 5.15.

12. Calculate the original area of the specimen and use it with the maximum load

recorded to calculate the ultimate compressive strength.

Fig. 5.15: Final test results.




4. Compression test results analysis

4.1 The compression test results for an aluminum test piece.

Type of material

Aluminum

Original Diameter, mm __________________________________________

Maximum Force (Load) in KN __________________________________________

Original Area, mm2

__________________________________________

__________________________________________

Ultimate compressive Strength(σu),

(N/mm2)

__________________________________________

__________________________________________

Modulus of elasticity

__________________________________________

__________________________________________

Yield stress __________________________________________

Activity 2

Plot the stress-strain diagram for the aluminium specimen using the sets of

data result from the test. The data will be given as force applied on the part

and extension of the part.

After plotting the curve, identify the following:

1- Elastic range.

2- Yield point.

3- Plastic range.

4- Ultimate compressive strength.

Note: you can use the spread sheet or any other similar application to

calculate the data and draw the stress-strain curve.



4.2 The tensile test results for a brass test piece.

Type of material

Brass



Original Area, mm2

__________________________________________

__________________________________________


(N/mm2)

__________________________________________

__________________________________________


__________________________________________

__________________________________________

__________________________________________

Yield stress __________________________________________

Activity 3

Plot the stress-strain diagram for the brass specimen using the sets of data

result from the test. The data will be given as force applied on the part and

extension of the part.


a. Elastic range.

b. Yield point.

c. Plastic range.

d. Ultimate compressive strength.



4.3 The tensile test results for a copper test piece.

Type of material

Copper



Original Area, mm2

__________________________________________

__________________________________________


(N/mm2)

__________________________________________

__________________________________________


__________________________________________

__________________________________________

__________________________________________

Yield stress __________________________________________

Activity 4

Plot the stress-strain diagram for the copper specimen using the sets of data




a. Elastic range.

b. Yield point.

c. Plastic range.




4.4 The tensile test results for a steel test piece.

Type of material

Steel



Original Area, mm2

__________________________________________

__________________________________________


(N/mm2)

__________________________________________

__________________________________________


__________________________________________

__________________________________________

__________________________________________

Yield stress __________________________________________

Activity 5

Plot the stress-strain diagram for the steel specimen using the sets of data




a. Elastic range.

b. Yield point.

c. Plastic range.




Activity 6

Analyze the stress -strain curves of the four tested material specimens

created earlier to find the following:

1. Which material has the highest compressive strength?

____________________________________________________________

2. Which material has the highest yield strength?

____________________________________________________________

5. References

1. MT3037 Universal Testing machine manual.MT3037-312 July 2007.

2. Modern engineering materials edition 1.

3. Engineering materials 1. “An introduction to Properties, Applications,

and Design”.

4. Modern Materials and Manufacturing Processes, R. G. Bruce, M. M.

Tomovic, J. E. Neeley, and R. R. Kibbe, Prentice Hall, 2nd Ed., 1987, pp

55-60.

5. Different internet sites.



Student’s notes

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ATM1112 Engineering materials module 5 - Maysaa Nazar · 2018-10-02 · ATM 1112 – Engineering Materials Module 5: Compression Test 13 Activity 6 ... MT3037 Universal Testing machine

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